Various bug fixes and minor improvements

- Fix static responder so it doesn't replace its own headers config,
  and instead replaces the actual response header values
- caddyhttp.ResponseRecorder type optionally buffers response
- Add interface guards to ensure regexp matchers get provisioned
- Use default HTTP port if one is not explicitly set
- Encode middleware writes status code 200 if not written upstream
- Templates and markdown only try to execute on text responses
- Static file server sets Content-Type based on file extension only
  (this whole thing -- MIME sniffing, etc -- needs more configurability)

modules/caddyhttp/caddyhttp.go

@@ -265,7 +265,12 @@ func (app *App) automaticHTTPS() error {
 				if err != nil {
 					return fmt.Errorf("%s: invalid listener address: %v", srvName, addr)
 				}
-				httpRedirLnAddr := joinListenAddr(netw, host, strconv.Itoa(app.HTTPPort))
+
+				httpPort := app.HTTPPort
+				if httpPort == 0 {
+					httpPort = DefaultHTTPPort
+				}
+				httpRedirLnAddr := joinListenAddr(netw, host, strconv.Itoa(httpPort))
 				lnAddrMap[httpRedirLnAddr] = struct{}{}
 
 				if parts := strings.SplitN(port, "-", 2); len(parts) == 2 {